refactor: перевёл цвета на CSS-переменные

frontend/src/components/ui/LectureCard.vue

@@ -130,7 +130,7 @@ function goDetail() {
 }
 .lecture-card:hover {
   transform: translateY(-3px);
-  box-shadow: 0 12px 40px rgba(0, 0, 0, 0.12), 0 0 0 1px rgba(34,197,94,0.2);
+  box-shadow: 0 12px 40px var(--color-black-a12), 0 0 0 1px var(--color-primary-a20);
 }
 .card-header {
   display: flex;
@@ -145,8 +145,8 @@ function goDetail() {
   font-weight: 600;
   color: var(--color-primary-dark);
 }
-.seats-low { color: #EA580C; }
-.seats-zero { color: #DC2626; }
+.seats-low { color: var(--color-orange-deep); }
+.seats-zero { color: var(--color-error-dark); }
 .card-title {
   font-size: 15px;
   font-weight: 700;
@@ -203,8 +203,8 @@ function goDetail() {
   font-size: 13px;
 }
 .btn-registered {
-  background: rgba(34,197,94,0.12);
-  border: 1px solid rgba(34,197,94,0.3);
+  background: var(--color-primary-a12);
+  border: 1px solid var(--color-primary-a30);
   border-radius: var(--radius-sm);
   color: var(--color-primary-dark);
   padding: 7px 14px;
@@ -213,8 +213,8 @@ function goDetail() {
   cursor: default;
 }
 .btn-disabled {
-  background: rgba(100,116,139,0.1);
-  border: 1px solid rgba(100,116,139,0.2);
+  background: var(--color-slate-500-a10);
+  border: 1px solid var(--color-slate-500-a20);
   border-radius: var(--radius-sm);
   color: var(--color-text-secondary);
   padding: 7px 14px;